Diet Or Exercise: What Matters More For Weight Loss?

“Exercise doesn’t matter. You just have to eat less” 

“Diet doesn’t matter much, as long as you exercise.”

A new study in the Journal of Nutrition says being more active not only won’t help you lose weight, it won’t even burn extra calories overall, at least in kids. The authors found that active kids and sedentary kids burned the same amount of calories, just doing different things. The active kids – rural Ecuadorian children who did a lot of subsistence farming activity – burned fewer calories when active, compared with the sedentary kids from “peri-urban” Ecuador.

Conversely, when the active kids were at rest, they burned more calories than the city kids did, so over the course of the day, they all burned about the same number of calories.

There were no differences between the two groups of kids with respect to height, weight, or BMI, but here’s where they did differ:

  • Active kids had less total body fat and percent body fat.
  • Active kids also had significantly more “fat-free mass” (read: muscle)

Hmmm, doing more laborious activity, they had more muscle and less body fat than their sedentary counterparts, but still didn’t burn any more calories at the end of the day? Seems odd?

I’m not surprised, and here’s why:

The kids doing the farm labor every day are in better physical condition. Their greater muscle mass and lower fat percent attest to this. Their bodies have adjusted to doing more physical activity by becoming more efficient with how they spend calories. The result: less difference between the energy needed for their activity and what they burn when they’re sitting.

Take an extreme example: a 150-pound runner who runs 10 miles a day, and a 150-pound sedentary guy who never exercises. Who is going to exert more effort on a 10-mile run? The sedentary guy of course, because his body isn’t conditioned for it. The runner’s body just sees it as another typical day, whereas the sedentary guy is gasping for air after a half-mile. The runner still burns calories while running, to be sure, but the sedentary guy burns more.

On the other hand, the runner may also burn a few more calories when at rest, because his metabolism doesn’t slow down to the degree the sedentary guy’s does. The runner’s body is anticipating getting back to physical work before long.

Is exercise useless?

Hardly – and we shouldn’t entertain that thought. Being physically active has endless benefits, and the study’s authors say so. However, their suggestion that overweight and obesity are driven primarily by diet, with a minor – if any – role played by physical activity, is not shared universally, and definitely not by me. I CANNOT separate the two.

Diet & activity changes often happen simultaneously, making it difficult to know which one has more influence. When kids (and adults) move to urban centers and do less physical activity, their diets typically also change to include more refined grains, and added sugar and fat, and fewer fruits and vegetables. They also snack more. They also do far less physical activity.

Instead of thinking it’s “either/or”, let’s try a different approach: Look at how people successfully lost weight and kept it off.

Enter the National Weight Control Registry (NWCR)

The NWCR, started in 1994 by James Hill and Rena Wing, has amassed a database of over 10,000 people. To qualify for inclusion, you must have lost at least 30 pounds and maintained the loss for at least a year, all objectively documented, so no fakes here. The NWCR has published many research papers about the results, finding that people lost weight in a wide variety of ways, yet there were surprisingly common factors about how weight loss was maintained. Just a few:

  • 47 out of 50 have increased their physical activity, most commonly by walking.
  • 9 in 10 exercise an average of 1 hour a day.
  • 49 out of 50 did modify their food intake in some fashion.
  • They’re doing fewer sedentary activities: 6 in 10 watch less than 10 hours of TV per week(!)

Cut-To-The-Chase Takeaway

Diet and physical activity: we all need to be mindful of both – for our health, our weight, and our enjoyment of life. Let’s make a point of enjoying the benefits of each, and be glad we can.

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